1. Field of the Invention
This invention pertains to esters of 2,2,4-trimethyl-1,3-pentanediol and benzoic acid or alkyl-substituted benzoic acids; to processes for making said esters; and to the use of said esters as stain-resistant plasticizers for poly (vinyl chloride) and other polymers, especially for poly (vinyl chloride)-based floor-covering compositions.
2. Description of the Prior Art
Many polymeric resins, such as vinyl chloride polymers by way of example, are hard and even brittle in their natural state, in the absence of plasticizers. Although such unplasticized resins can often be used to manufacture useful articles of commerce, such as pipes, house siding, phonograph records, and so forth, for many other applications plasticizers are required in order to lower processing temperatures or to impart flexibility and softness to end products made from such resins. In addition to improving processability and imparting flexibility, suitable plasticizers must be compatible with the resin, must be thermally stable during processing and under end-use conditions, should not impart substantial color or odor, and should be permanent, i.e., should be resistant to removal from the resin due to volatilization, extraction by solvents, or migration into any material in contact with the plasticized resin.
Polymers and copolymers of vinyl chloride are widely used as plasticized compositions, and a very large number of compounds have been found to be useful, in varying degrees, as plasticizers for such resins. In particular, the most useful of such plasticizers include diesters of alkanols and dicarboxylic acids, polyesters derived from diols and dicarboxylic acids, and, to a lesser extent, diesters of diols and monocarboxylic acids.
One of the major applications for plasticized vinyl chloride compositions is as floor coverings and wall coverings, for purposes of both protection and decoration. In these applications in particular, a further required attribute of a suitable plasticizer is to impart resistance to staining when contacted by such things as road tar, crayons, shoe polish, foodstuffs, and so on.
Floor and wall covering compositions based on vinyl chloride polymers are manufactured by various methods, especially by calendering or by spread-coating of a liquid dispersion--a plastisol or an organosol--onto a substrate. In the latter case, a still further requirement must be met in order for a plasticizer to be suitable: the plasticizer must have a sufficiently low viscosity to impart fluidity to the plastisol or organosol, must have solvating power for the resin at elevated temperatures sufficient to readily fuse resin and plasticizer into a coherent mass but, at the same time, its solvating power for the resin at ordinary room temperature should be low enough to avoid undue increase in the viscosity of the dispersion after preparation and during storage. A large and rapid viscosity increase may make it difficult, or impossible, to spread the dispersion properly onto the substrate. As an example, butyl benzyl phthalate has many of the desirable attributes of a plasticizer for vinyl chloride polymers, including fairly good stain resistance, but its solvating power at ordinary temperatures causes rapid viscosity increase in plastisols and therefore limits its applicability in such dispersions.
There are numerous disclosures in the prior art of plasticizers for vinyl chloride polymers (PVC) and other resins that are said to impart stain resistance, some of which are esters of benzoic acid and some of which are diesters of 2,2,4-trimethyl-1,3-pentanediol (hereinafter referred to as TMPD). In U.S. Pat. No. 3,158,585 Kelso et al discloses phthalic acid esters of various alcohols as stain resistant plasticizers. In U.S. Pat. No. 3,160,599 Scullin discloses the stain resistance of the monoisobutyrate monobenzoate ester of TMPD. Bailey et al, J. Amer. Oil Chem. Soc. vol. 53, 176-178 (1976) reports on the utility as PVC plasticizers of mixed esters of ethylene glycol, diethylene glycol, and 2-butene-1,4-diol wherein one of the ester moieties was benzoate. U.S. Pat. Nos. 4,024,164; 4,074,058; and 4,107,192 to Bailey contain related disclosures.
Wickson et al, Soc. Plastic Eng. Preprint, Annual Technical Conference, p. 238-42 (1969) compares the properties as PVC plasticizers of ethylene glycol diesters. In U.S. Pat. No. 2,454,274 Daly et al discloses the utility of ethylene glycol acetate benzoate as a plasticizer for esters and ethers of cellulose.
In U.S. Pat. Nos. 2,700,656 and 2,766,266 Emerson et al discloses diesters of substituted 1,5-pentanediols, in which one ester group is an aromatic acid moiety and the other an aliphatic acid moiety. In U.S. Pat. No. 3,072,591 there are disclosed, as PVC plasticizers, aromatic-aliphatic carboxylic acid esters of a polymethylolalkane.
U.S. Pat. 3,433,661 to Maggart et al discloses complex monoesters derived from aromatic hydrocarbons, formaldehyde, and monocarboxylic acids as stain resistant plasticizers. U.S. Pat. No. 3,562,300 to Chao et al discloses the use of neoalkylpolyol esters of neoacids and straight or branched chain aliphatic acids as plasticizers.
In U.S. Pat. No. 3,652,610 Coopersmith discloses plasticizers derived from the reaction of a hindered acid glycol monoester and di- or tri-basic acids. Japanese Patent Publication 52-101253 discloses as plasticizers polyalkylene glycol esters containing 1-14 ether bonds, and having one benzoic acid ester group and one aliphatic acid ester group. In U.S. Pat. No. 4,656,214 Wickson discloses stain resistant plasticizers that are diesters of ethylene glycol, propylene glycol, or 1,4-butanediol in which one ester group is a benzoate or toluate moiety, and the other a neoacid moiety. This reference also contains an incidental disclosure of plasticizer that is a mixture of diesters of TMPD, including, TMPD dibenzoate as one of the lesser components.
In processes involving TMPD as a reactant, the thermal instability of this glycol under various conditions must be taken into account. Thus, the review of TMPD in the Encyl. Chem. Tech. (Kirk-Othmer), 2nd Ed. p. 679 (1966) points out that TMPD diesters undergo pyrolysis to the corresponding monoesters of 2,2,4-trimethyl-3-penten-1-ol. P. Morison and J. E. Hutchins, Am. Chem. Soc., Div. Org. Coatings Plastics Chem; Preprints 21, No. 1, 159-70 (1961); CA. 57, 15272 e, reported that, among various glycols studied, TMPD was the most prone to thermal degradation.
B. Yoemans, Brit. 1,290,094 (1972); CA. 78, 15503a produced 2,2,4-trimethylpenten-1-isobutyrate by acid catalysed dehydration of a mixture of TMPD isobutyrates, TMPD diisobutyrat and TMPD itself. In related work, M. Mazet and M. Desmaism, Brut, Bull. Soc. Chim. Fr. 1971 (7) 2656; CA. 75, 117725e reported that the acid-catalysed dehydration of the secondary hydroxyl group of TMPD is also accompanied by some methyl migration from C.sub.2 to C.sub.3.
Instability under basic conditions also was described by E. Harrer and K. Ruhl, Ger. 1,011,865 (1957). Thus heating TMPD with potassium hydroxide at 145.degree. C. reversed the process, of its formation by producing isobutyraldehyde, isobutyl alcohol and isobutyrate ion.
Despite the inherent instability associated with the structure of TMPD, fair-to-excellent results have been achieved in preparing aliphatic diesters, with acidic conditions appearing the most favorable. Thus, TMPD diacetate was prepared in 93% yield by H. Nosler and H. Schnegelberger, U.S. Pat. No. 3,671,654 (1967); CA. 78, 75876j, by the action of acetic anhydride at 120-130.degree. C. in the presence of p-toluenesulfonic acid. TMPD diformate has also been prepared using sulfuric acid as a catalyst for the reaction of TMPD with excess formic acid by R. Boden and M. Licciardello, U.S. Pat. No. 4,405,646 (1983); CA. 100, 5039n, but no yield was reported.
A. Bell, U.S. Pat. No. 2,625,563 (1953); CA. 47, 11229b, prepared the bis 2-ethylbutanoic and 2-ethylhexanoic esters at 60% and 42% yields respectively via uncatalysed esterifications of TMPD with the corresponding acids at 200-210.degree. C. The bis decanoic and tridecanoic esters were also prepared by A. Bell and G. Lappin, Brit. 767,455; CA. 51, 13379i, but no experimental details were provided.
TMPD diesters have also been prepared by transesterification. Thus in Japan Kokai Tokkyo Koho JP No. 58 49377 (83 49 377) (1983); CA. 99, 53768g, the p-toluenesulfonic acid-catalysed reaction of TMPD with ethylene carbonate at 110.degree. C. led to a 93% yield of the cyclic carbonate ester, i.e. a disubstituted TMPD ester derivative.
T. Ogawa et al, Japan Kokai Tokkyo Koho 79 46708 (1979); CA. 91, 140357a, prepared TMPD diisobutyrate in 96% yield via the transesterification reaction of TMPD with isobutyl isobutyrate using tin or titanium, Lewis acid-type catalysts at 120-250.degree. C. With a basic system employing sodium hydroxide catalysis, the yield was only 64%. A similar basic system for preparing TMPD diisobutyrate from TMPD and isobutyl isobutyrate, in the presence of sodium hydroxide in isobutyl alcohol at 120-170.degree. C., was employed by T. Kojima et al., Japan Kokai 74 94620 (1974); CA. 82, 139395u. No yield was reported, however.